Conventionally, a headrest drive control device (for example, see Patent Document 1 (pp. 2-6, FIGS. 1-4)) is known as a technique for adjusting the position of a headrest provided on a seat of a vehicle such as an automobile, etc. The headrest drive control device monitors a capacitance between a pair of electrodes embedded in the ceiling of the vehicle and in the headrest, and adjusts the position of the headrest by judging presence or absence of a head based on the amount of change in the capacitance which occurs when scanning is performed by driving the headrest upward from a lower end.
A headrest driving device (for example, see Patent Document 2 (pp. 3-8, FIGS. 1-4)) adjusts the position of a headrest to a place at which outputs from four capacitor plates embedded in the headrest are balanced.
A headrest adjusting device (for example, see Patent Document 3 (pp. 3-6, FIGS. 1-5)) monitors a capacitance between one electrode arranged in a headrest and a head, and adjusts the position of the headrest by judging presence or absence of a head based on the amount of change in the capacitance which occurs when scanning is performed by driving the headrest upward and downward.
A device for adjusting a headrest of a vehicle (for example, see Patent Document 4 (pp. 2-3, FIGS. 1-3)) adjusts the position of a headrest by using two or three capacitor plates arranged in the headrest and measuring a capacitance between a head and the capacitor plates.